Axial Diffuser Flow Control Device

ABSTRACT

An axial diffuser for a gas turbine includes diffuser walls that define diffuser channels receiving compressor discharge air. The diffuser walls diverge in a flow direction. A flow control device is disposed in the diffuser channels and includes a plasma controller that serves to ionize airflow in the diffuser channels.

BACKGROUND OF THE INVENTION

The invention relates generally to gas turbines and, more specifically,to an axial diffuser in a gas turbine including a plasma controller tocontrol air flow.

Conventional gas turbine combustion systems employ multiple combustionchamber assemblies to achieve reliable and efficient turbine operation.Each combustion chamber includes a cylindrical combustor, a fuelinjection system, and a transition piece that guides the flow of the hotgas from the combustor to the inlet of the turbine. Generally, a portionof the compressor discharge air is introduced directly into thecombustor reaction zone to be mixed with the fuel and burned. Thebalance of the airflow serves either to quench the flame prior to thecombustor discharge entering the turbine, or to cool the wall of thecombustor and, in some cases, the transition piece.

In systems incorporating impingement cooled transition pieces, a hollowsleeve surrounds the transition piece, and the sleeve wall is perforatedso that compressor discharge air will flow through the cooling aperturesin the sleeve wall and impinge upon (and thus cool) the transitionpiece.

Because the transition piece is a structural member, it is desirable tohave lower temperatures where the stresses are highest. This has provendifficult to achieve, but an acceptable compromise is to have uniformtemperatures (at which the stresses are within allowable limits) allalong the length of the transition piece. Thus, uniform flow pressuresalong the impingement sleeve are desirable to achieve the desireduniform temperatures.

Substantially straight axial diffusers are typically utilized in gasturbines at the compressor discharge location.

A typical problem associated with existing diffuser configurations isflow separation. The flow gets detached from the surface creating lossesand reducing pressure recovery. Efforts have been made to have anaggressive design of the diffuser for reducing its length of providing asteeper angle and by diverging the annulus in two stages. The steeperangle, however, creates more flow separation, thereby reducing thepressure recovery. Current methods of flow control are achieved bymechanical means, which are complicated, add weight, have volume and aresources of noise and vibration. Also, existing devices are typicallycomposed of mechanical parts that wear away and that may break down.

It would be desirable to eliminate the problems with existing deviceswhile effectively controlling the flow profile.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, an axial diffuser for a gas turbine includesdiffuser walls that define diffuser channels receiving compressordischarge air. The diffuser walls diverge in a flow direction. A flowcontrol device is disposed in the diffuser channels. The flow controldevice includes a plasma controller that serves to ionize airflow in thediffuser channels.

In another exemplary embodiment, a flow control device is cooperablewith an axial diffuser in a gas turbine and includes the plasmacontroller that serves to ionize airflow through the axial diffuser.

In still another exemplary embodiment, a method of controlling flow in agas turbine axial diffuser includes the steps of positioning a flowcontrol device in diffuser channels of the axial diffuser, where theflow control device includes a plasma controller; and applying a currentto the plasma controller to ionize airflow in the diffuser channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a gas turbine;

FIG. 2 is an enlarged view of a portion of the gas turbine illustratedin FIG. 1;

FIGS. 3-5 show exemplary turbine configurations including an axialdiffuser with a plasma controller; and

FIG. 6 is a schematic illustration including an energized plasmacontroller and a boundary layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view, in cross-section, of a portion of a gasturbine, illustrating the environment in which an embodiment of thepresent invention operates. The gas turbine 100 includes a compressorsection 105, a combustion section 150, and a turbine section 180.Generally, the compressor section 105 includes a plurality of rotatingblades 110 and stationary vanes 115 structured to compress a fluid. Thecompressor section 105 may also include at least one extraction port120, an inner barrel 125, a compressor discharge casing 130, a marriagejoint 135, and a marriage joint bolt 137.

Generally, the combustion section 150 includes a plurality of combustioncans 155 (only one is illustrated), a plurality of fuel nozzles 160, anda plurality of transition sections 165 (only one is illustrated). Theplurality of combustion cans 155 may be coupled to a fuel source (notillustrated). Within each combustion can 155, compressed air is receivedfrom the compressor section 105 and mixed with fuel received from thefuel source. The air and fuel mixture is ignited and creates a workingfluid. The working fluid generally proceeds from the aft end of theplurality of fuel nozzles 160 downstream through the transition section165 into the turbine section 180.

Generally, the turbine section 180 includes a plurality of rotatingcomponents 185, a plurality of stationary components 190, and aplurality of wheelspace areas 195. The turbine section 180 converts theworking fluid to a mechanical torque.

Typically, during the operation of the gas turbine 100, a plurality ofcomponents experience high temperatures and may require cooling orpurging. These components may include a portion of the compressorsection 105, the marriage joint 135, and the plurality of wheelspaceareas 195.

The extraction port 120 draws cooling fluid from the compressor section105. The cooling fluid bypasses the combustion section 150, and flowsthrough a cooling circuit 200 (illustrated in FIG. 2), for cooling orpurging various components, including the marriage joint 135, and atleast one of the plurality of wheelspace areas 195.

FIG. 2 is a close-up view of a section of the gas turbine illustrated inFIG. 1. The flow path of the cooling circuit 200 may start at theextraction port 120 (illustrated in FIG. 1), flow through a portion ofthe compressor discharge casing 130 and the inner barrel casing 125,through to a cavity at the aft end of the compressor section 105. Next,the cooling circuit 200 may reverse direction, flowing past the marriagejoint 135, past the seal system components 140, to the wheelspace area195.

An axial diffuser 12 is provided at the compressor discharge location todistribute compressor discharge air along the impingement sleevesurrounding the transition piece. The axial diffuser 12 includesdiffuser walls that define diffuser channels 14 that receive thecompressor discharge air. As shown, the diffuser walls diverge in a flowdirection (shown by arrows in FIGS. 3-5). A flow control device such asa plasma controller 2 is disposed in the diffuser channels. The plasmacontroller 2 serves to ionize air flow in the diffuser channels. Theplasma controller 2 is provided with an anode 3 and a cathode 4 or othersuitable electrodes, and an energy source 7 (FIG. 6) provides a currentbetween the electrodes 3, 4. In one arrangement, the electrodes consistof two low-diameter wires flush-mounted on the surface in the diffuserchannels.

In use, the fluid/air in the diffuser will get ionized, and in ambientair, an electric wind is created tangentially to the diffuser wall. Theeffect is used to reduce the flow separation, providing effective flowcontrol and reduced pressure drop. As shown, the electrodes can bemounted to the inner surface of the axial diffuser casing.

The air flow direction can be altered in different channels based on theaerodynamic shape of the diffuser, hence making the airflow conform tothe shape of the diffuser. Moreover, a decreased amount of air duringreduced load on the turbine can be made to accelerate through thediffuser to thereby further control turbine performance. Additionally,redirecting the amount and the nature of the flow may serve to controlthe impingement of air on the combustion hardware.

An exemplary plasma controller 2 is illustrated in FIG. 6. The plasmacontroller 2 is secured to the diffuser walls, preferably mounted to aninner surface of the axial diffuser casing. The plasma controller 2includes first and second electrodes 3, 4 separated by a dielectricmaterial 5. The dielectric material 5 is disposed within spanwiseextending grooves 6 in the diffuser walls. A power supply 7 is connectedto the electrodes 3, 4 to supply a high voltage potential to theelectrodes. Preferably, the power supply 7 is a direct current powersupply.

When the current amplitude is large enough, the gas flow 19 ionizes in aregion of largest electric potential forming the plasma 90. The plasmacontroller 2 produces an outer surface conforming plasma 90 which coversa substantial portion of the diffuser channels. The plasma 90 generallybegins at an edge 102 of the first electrode 3, which is exposed to thegas flow 19, and spreads out over an area 104 projected by the secondelectrode 4, which is covered by the dielectric material 5. The plasma90 in the presence of an electric field gradient produces a force on thegas flow 19 located between the diffuser surface and the plasma 90inducing a virtual aerodynamic shape that causes a change in thepressure distribution over the diffuser surface.

The use of plasma flow control in an axial diffuser serves to reduceflow separation without complicated mechanical devices that add weightand can be sources of noise and vibration. Effective flow control and areduced pressure drop can be advantageously achieved by the applicationof current between the plasma controller electrodes. The improvedpressure recovery results in higher and more efficient power generation.Additionally, the device is suitable for retrofitting on existingturbines.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An axial diffuser for a gas turbine, the axialdiffuser comprising: diffuser walls that define diffuser channelsreceiving compressor discharge air, the diffuser walls diverging in aflow direction; and a flow control device disposed in the diffuserchannels, the flow control device including a plasma controller thatserves to ionize airflow in the diffuser channels.
 2. An axial diffuseraccording to claim 1, wherein the plasma controller comprises two wiressecured to the diffuser walls and an energy source providing a currentbetween the two wires.
 3. An axial diffuser according to claim 2,wherein the energy source comprises a direct current power supply.
 4. Anaxial diffuser according to claim 1, wherein the plasma controllercomprises first and second electrodes secured to the diffuser walls andseparated by a dielectric material, and an energy source connected tothe electrodes.
 5. An axial diffuser according to claim 1, wherein theplasma controller comprises an anode and a cathode secured to one of thediffuser walls, and wherein the cathode is disposed downstream of theanode.
 6. A flow control device cooperable with an axial diffuser in agas turbine, the flow control device comprising a plasma controller thatserves to ionize airflow through the axial diffuser.
 7. A flow controldevice according to claim 6, wherein the plasma controller comprises twowires secured to walls of the diffuser and an energy source providing acurrent between the two wires.
 8. A flow control device according toclaim 7, wherein the energy source comprises a direct current powersupply.
 9. A flow control device according to claim 6, wherein theplasma controller comprises first and second electrodes secured to wallsof the diffuser and separated by a dielectric material, and an energysource connected to the electrodes.
 10. A flow control device accordingto claim 6, wherein the plasma controller comprises an anode and acathode secured to one of the diffuser walls, and wherein the cathode isdisposed downstream of the anode.
 11. A method of controlling flow in agas turbine axial diffuser, the method comprising: positioning a flowcontrol device in diffuser channels of the axial diffuser, the flowcontrol device including a plasma controller; and applying a current tothe plasma controller to ionize airflow in the diffuser channels.
 12. Amethod according to claim 11, wherein the plasma controller includesfirst and second electrodes secured in the diffuser channels andseparated by a dielectric material, and an energy source connected tothe electrodes, the method further comprising creating an electric wind.13. A method according to claim 12, wherein the applying step ispracticed by applying a direct current between the first and secondelectrodes.
 14. A method according to claim 11, wherein the positioningstep is practiced by securing two wires to walls of the diffuser.
 15. Amethod according to claim 11, comprising altering an air flow directionin different channels based on an aerodynamic shape of the diffuser,thereby making the air flow conform to the shape of the diffuser.
 16. Amethod according to claim 11, comprising accelerating a decreased amountof air during reduced load on the turbine through the diffuser tothereby further control turbine performance.
 17. A method according toclaim 16, comprising redirecting an amount and nature of the flow tocontrol impingement of air on the combustion hardware.